Wtest.exs

defmodule WithTest do

  def ok(x), do: {:ok, x}
  def error(x), do: {:error, x}
end

IO.inspect   with {:ok, x} <- WithTest.ok(1),
                  {:ok, y} <- WithTest.ok(2),
                  do: {:ok, x + y}
IO.puts "----------------------------\n"

IO.inspect   with {:ok, x} <- WithTest.ok(1),
                  {:ok, y} <- WithTest.error(2),
                  do: {:ok, x + y}


defmodule WithTest1 do
  def plus(x) do
    if x + 1 == 2 do
      {:ok,x}
    end
  end

  def pluss(x) do
    if x + 1 == 2 do
      {:ok, x}
    else
      {:error}
    end
  end

  def run do
    with  {:ok, x} <- WithTest1.plus(2),
          {:ok, y} <- WithTest1.pluss(1) do

          {:ok, x + y}
      else
        :error -> {:error, :wrong_data}
        nil -> {:error, :wrong_data1}
      end
  end
end
IO.inspect WithTest1.run



ref
https://stackoverflow.com/questions/34210281/how-to-use-the-with-keyword-in-elixir-and-what-is-it-for
https://gist.github.com/josevalim/8130b19eb62706e1ab37
https://hexdocs.pm/elixir/master/Kernel.SpecialForms.html#with/1
https://hexdocs.pm/elixir/master/WithClauseError.html